If parody is a gauge of the instantly iconic, then Hannibal is already the resonant film of the year. The posters showing Anthony Hopkins's glimmering red eye had just appeared in the London Underground when they were joined by an almost identically sinister ad for Peperami. The sequel to The Silence Of The Lambs is undoubtedly an Event. The film opens in America on 9 February, 10 years to the week since the opening of The Silence Of The Lambs, and arrives in the UK seven days later.

Ever since filming started last year, Hannibal has been a fanatically closely guarded project, but there were still stories leaking from the set about citizens of Florence demanding the 'vulgar horror film' be driven from their august city. Angry Florentines notwithstanding, the film reaches our screens just as its director, Ridley Scott, is the focus of a massive Oscar push for Gladiator.

At exclusive screenings in the States audiences have been heard to gasp in horror at some of the more atrocious scenes. And don't think you know the ending, just because you've read Thomas Harris's hugely successful book: they've changed it for the film, and made the very few people who have seen previews promise not to reveal what happens.

Hannibal starts with Clarice Starling (Julianne Moore replacing Jodie Foster) falling out of favour with the FBI after a messy narcotics operation. The action then switches to Italy, where Lecter is relishing life as Dr Fell, a museum curator (the previous occupant of the job having vanished).

Despite his outré taste in food, Lecter is now the hero: he only consumes the truly deserving, dispatching them with finely wrought pay-off lines. The hideous criminal here is Lecter's wheelchair-bound, disfigured former patient and victim, Mason Verger, played by Gary Oldman, practically unrecognisable under make-up. Verger concocts an elaborate trap for Lecter after he returns to the US following one tasting too many. Minor villainy is provided by Ray Liotta as Starling's unpleasant boss, and veteran Italian actor Giancarlo Giannini as a greedy detective.

Not surprisingly, many of Harris' s more gruesome scenes haven't made it to screen, but there are still crucial stomach-churning episodes, including an enduringly nasty climax. Lecter, says Hopkins, is 'mellower' now, while Moore's Starling is a complex, grown-up woman whose once bright career never took off.

Scott says that 'wit' is central to his film, so the gory humour that was a lesser thread in Jonathan Demme's movie is pushed to the fore here. 'I shall be very disappointed if I hear that people aren't smiling,' says Scott. 'When they're not screaming.'

That there is a fuss around this film is no surprise when you think back to the massive impact The Silence Of The Lambs had. It became one of only three films ever to pick up the four big Oscars (best picture, director, actor and actress) and also won best adapted screenplay. It turned Hopkins at the age of 53 from another distinguished British actor taking jobbing film roles into a genuine Hollywood star. People described it as one of the most terrifying films they had ever seen. And beyond the visceral impact, it was seen as a feminist landmark thanks to Foster's Clarice.

So a sequel always seemed likely, but Harris wouldn't be rushed into writing his book, and Hannibal wasn't published until June 1999. All things considered, the gap from publication to screen has been a short one. More so when you discover there were legal dramas over the complex issue of who owned the characters.

Producer Dino De Laurentiis eventually paid a record $10 million to pick up the option on Harris's Hannibal, and all that remained was to re-assemble the winning team. Only it didn't happen.

Demme turned down the project, allegedly because he found the new material 'lurid' - Scott came in after De Laurentiis had hastily reassured the confused director that this Hannibal wasn't another Roman epic. Screenwriter Ted Tally also passed, worrying about the novel's excesses - although he's now meant to be reworking Red Dragon (the first Hannibal novel, released in 1986 as Manhunter). And then Jodie Foster - having asked for rewrites on the script (David Mamet did a draft, followed by Steve Zaillian) - also passed, which seemed to put the whole project under threat. Hopkins was apparently furious, and 81-year-old De Laurentiis 'outraged'. At short notice she was replaced by Julianne Moore, someone who disappears into parts rather than generating the off-screen fascination that Foster does.

All sorts of explanations have been put forward about why Foster said no: she wanted to direct another film; maybe she had been offered half the cut of the profits that Hopkins was or her agent was insisting on $20 million plus 15 per cent of the profits; or that Clarice has to unwillingly do something truly offensive at one point.

But there is no mystery about why a return to playing Starling would have been less appealing. Jodie Foster was the star of The Silence Of The Lambs: she's the image on the poster and she had most of the screen time. More than that, the film represents a therapeutic path for Starling (Lecter is, after all, a psychiatrist), as she learns to deal with both her childhood demons and her class anxieties. Even the title comes from one of her early experiences.

Perhaps the problem for Foster was that Clarice is not quite so central a character in Hannibal. Rather than being about how Lecter can help Starling, Hannibal is about how the struggling Starling fits into Lecter's plans: this time around, the cannibal takes centre stage.

It is some kind of testament to the power of the franchise that a director of Scott's weight was willing to step in when Demme turned down the project. The auteur sequel is a narrow category: the Alien series, and the curious case of Mission: Impossible 2 are two examples that spring to mind.

The change of director made it inevitable that Hannibal would be a different beast from its predecessor, if only because Scott is the kind of director who couldn't mimic someone else's style if he tried.

The shoot was quick for a film of this size, but it wasn't easy. There were those irate Florentines, for a start. A Popular Party spokesmen proclaimed: 'This film adds nothing to Florence's world prestige. We believe that instead the city would become the setting for morbid thrills and vulgar horror.'

Then there was Gary Oldman, who couldn't decide whether he should try to get equal billing with Hopkins, or have his name kept off the credits entirely (he opted for the latter). And Moore had a tough time: she broke her toe just before she was meant to get in shape for the part, she was profoundly uncomfortable using guns, and more uncomfortable still working with the pack of giant wild boars for one of the film's key scenes.

Ultimately, though, this is Hopkins's vehicle, a license for him to have fun on screen, leering out from under a Panama hat. Some readers may remember that about 18 months ago Hopkins announced his retirement from the movies. With an impressive sense of timing, his decision to reconsider coincided with the most eagerly anticipated performance of his career. He's no fool, clearly.

The book: Fastest-selling hardback adult fiction ever in the UK, selling one million copies to date. On completion, Thomas Harris sent copies of the finished manuscript to Jodie Foster, Anthony Hopkins and director Jonathan Demme as well as to his publisher.

Anthony Hopkins: 'Playing Hannibal was a matter of speaking in a monotone and not blinking.'